As the SC pointed out, there are several types of RAID configurations. RAID 0, RAID 1, RAID 0+1, RAID 3 and RAID 5 are the most common. If you are planning to use a RAID Array in a gaming rig, DO NOT use a software based RAID manager. This uses precious CPU time that could otherwise be spent handling the game software.
I personally use a 4 disk IDE RAID 5 Array on my AMD XP 2700+ rig and it works very well. RAID 5 however is not really built for performance but rather more for redundancy. I have high enough system specifications that the small hit I take in drive write operations is really not noticeable. I am using a hardware RAID controller by 3Ware. Specifically the Escalade 7500-8 model with 4 80GB Western Digital 7200 RPM 8MB cache hard drives. Since I run my system 24/7 due to SETI@Home processing, I opted for the protection RAID 5 offers. My system can sustain 1 failed hard drive and still remain fully operational. If I have a drive fail on me, I will take a small hit in performance (nothing to drastic) until I replace the bad drive and rebuild the array.
My serious recommendation for a gaming platform if you do not need the redundancy offered by RAID 5 is to go RAID 0. RAID 0 is also known as striping. It works essentially the same way as RAID 5 in that it writes the data across all the disks in the array. Unlike RAID 5 however, if one drive were to fail your entire array crashes and you lose your data. RAID 0 will give you about the best drive performance you can get for read operations since it can pull data from all of the hard drives on the array at once. Typically when you are running games, this is usually what is occuring. Write operations are much faster than RAID 5 because unlike RAID 5, it does not have to worry about writing the ECC (recovery) information to the Array.
RAID 1 is called "Mirror" because you essentially have 1 drive acting as a complete mirror (invisible) to your active hard drive. In the event of a failure to your main hard drive, the RAID 1 mirror automatically kicks in without interruption. This offers you no performance advantage what-so-ever (only redundancy) and is not something the average performance hungry gamer would want.
When deciding to build an array the second biggest decision (after choosing your hardware RAID controller) you need to make is finding the right hard drives to operate in your array. Do you go for IDE or SCSI? IDE is generally cheaper and with the new performance standards on these drives the average gamer really won't need to look at SCSI. SCSI offers the absolute best performance but the price is extremely high per drive. Whichever technology you choose, make sure you get a drive that can operate at fast RPM speeds and has as much on board drive cache as you can get. These will give you a BIG boost to performance. You will also need to look at drive throughput. The typical IDE drive will function at ATA-100 or ATA-133 transfers. The 133 of course has faster throughput but this should not be your single deciding factor when purchasing a drive. You would be better off with an ATA-100 if you can get a drive with high RPM speed AND high drive cache for example.
Lastly, make sure your rig has a sufficient power supply to handle your big boy RAID array. My current system runs a 430 watt power supply. If you are still running a system at 300 watts or lower, it would be a good idea to invest in a higher end power supply before you embark on your RAID adventure.
This should about cover the basics. Happy hunting!
Torrellan